One thing I will caution about is "marina talk" about using Thompson's Water Seal to renew the waterproofing. When we had a Crealock 37 our Sunbrella began to "weep" some. The scuttlebutt was that Thompson's was dirt cheap and just the ticket. Being a skeptic about things that are too good to be true, I called North Sails, who had built the Bimini. Their rep said "If you want to see some world-class mildew, use Thompson's. If not, find a waterproofing with the highest silicone content that you can find, and wet the Sunbrella thoroughly with that." They sold a liquid, brush-on product aimed at commercial use, but she felt the cost would be prohibitive for a small job. We used a spray (Atsko Silicone Water-Guard) from a camping supply store which had 13% silicon, and it worked well, with a service life of about a year, cruising full-time in southern waters with the canvas always up.
We sold the Crealock after 5 years and bought an Atlantic 44 Long-Range Cruiser (aka a "trawler"). The previous owner had gone the Thompson's route. We fought heavy, yellow mildew for over a year. We would have to periodically scrub the underside of the Bimini when it would look so much like the roof of a limestone cave that it would give you the creeps. The lady at North had it spot on!
As someone has said, the stitching is another point to watch, but newer threads are quite sun-resistant. Just keep an eye on things and have a canvas worker restitch before the seam actually opens up. We had ours restitched 100%, one time, when it was about 8 years old. The waterproofing is the other maintenance area eventually. The fabric itself will last for many Years.
